THE SKELETON AND TEETH 131
relatively deeper in the Gorilla than in the Chimpanzee, and the crista galli is rudimentary or absent. At the sides of the fossa the roots of the orbits bulge up into the anterior cerebral fossa, but the roofs are more convex in the Chimpanzee. Xo ridge runs up from the fossa on the deep surface of the frontal bone as in the Chimpanzee. The presphenoid is grooved by the optic chiasma to a greater depth than in the Chimpanzee, and the sella turcica is overhung by the posterior clinoid processes. The cranial bones are considerably lightened by an extensive system of sinuses.
The frontal sinuses are separated by a septum. The sphenoidal sinus may be entire or subdivided and extends into the alisphenoids and pterygoid plates as in the Chimpanzee. The antrum of Highmore is large, and Owen (374) described it as follows: k*The vast antruin extends to the floor and inner wall of the orbit and into the malar bone; it communicates with the nostrils by a wide aperture, overarched by the inferior turbinal, and sometimes also by a smaller opening overarched by the turbinal process above. Its walls being broken away on the left side in the skull of an old male Tr. Gorilla, shows what appears to be the convex back part of a second wall of the antrum, about half an inch from the outer one, and which is cribriform or reticulate ; a portion of this convexity, removed vertically on the right side in the same skull, revealed light and delicate osseous texture . . . delicate bony plates and threads interlaced . . , and formed a reticulated inner wall."
The mandible is verv massive, and its rarni onlv
«. * k
diverge slightly. The ascending ramus is high and a